Climate Change Harp Seals Abandon Pups
July 22, 2013

Harp Seals Abandoning Their Pups Thanks To Climate Change

Lee Rannals for - Your Universe Online

Duke University scientists have determined that young harp seals off the eastern coast of Canada are at a greater risk of getting stranded than adult seals due to climate change.

Researchers wrote in the open-access journal PLOS ONE that declining sea ice is leaving baby harp seals stranded in greater numbers.

"Stranding rates for the region's adult seals have generally not gone up as sea ice cover has declined; it's the young-of-the-year animals who are stranding (those less than one year old)," said David Johnston, a research scientist at Duke's Nicholas School of the Environment. "And it's not just the weakest pups - those with low genetic diversity and presumably lower ability to adapt to environmental changes - that are stranding. It appears genetic fitness has little effect on this."

He said that harp seals rely on stable winter sea ice as a safe platform to give birth and nurse their young until the pups can go off on their own. However, in years with light ice cover, younger seals are being left to fend for themselves before they're ready.

Johnston and his colleagues expanded on a study published last year that found seasonal ice cover in all four harp seal breeding regions has declined by up to six percent since 1979. The team compared winter ice from 1992 to 2010 in a region off Canada's east coast with yearly reports of dead harp seal strandings along the US northeast coast that were grouped by gender and estimated age of the seal.

According to the latest analysis, in years when ice cover was reduced, stranding rates for younger seals rose sharply, even though stranding rates of adult seals remained relatively stable. The team also compared DNA samples from 106 harp seals that had been stranded ashore with those from seals that had been caught by fishing boats in the region during the same period.

"We used measures of genetic diversity to determine if the dead seals that came ashore were less fit than the presumably healthy ones that had been caught by fishermen, but found no difference," said Thomas Schultz, director of Duke's Marine Conservation Molecular Facility. "The stranded animals appear to have come from a genetically diverse population, and we have no evidence to suggest that genetic fitness played a role in their deaths."

The study found that male seals were stranded more frequently than females during the study period, and that this relationship was strongest during light ice years.

"Our findings demonstrate that sea ice cover and demographic factors have a greater influence on harp seal stranding rates than genetic diversity," said Brianne Soulen, who co-led the study while she was a master's degree student in marine ecology at Duke.

Kristina Cammen, a Duke PhD student who also co-led the study, said this study provided more context for how climate change is affecting younger animals during a crucial part of their life.